ANKARA, Oct 7 (Reuters) - Turkish authorities believe Saudi journalist Jamal Khashoggi was killed inside his country’s consulate in Istanbul last week, Turkish sources said, in what they described as the deliberate targeting of a prominent critic of the Gulf kingdom’s rulers.

Khashoggi, a former newspaper editor in Saudi Arabia and adviser to its former head of intelligence, left the country last year saying he feared retribution for his growing criticism of Saudi policy in the Yemen war and its crackdown on dissent.

On Tuesday he entered the Saudi consulate in Istanbul to get documents for his forthcoming marriage. Saudi officials say he left shortly afterwards but his fiancee, who was waiting outside, said he never came out.

“The initial assessment of the Turkish police is that Mr Khashoggi has been killed at the consulate of Saudi Arabia in Istanbul. We believe that the murder was premeditated and the body was subsequently moved out of the consulate,” one of two Turkish officials told Reuters on Saturday.

The Turkish sources did not say how they believed the killing was carried out.

A Saudi source at the consulate denied that Khashoggi had been killed at the mission and said in a statement that the accusations were baseless.

The Saudi source said that a security team including Saudi investigators had arrived in Istanbul on Saturday to take part in the investigation into Khashoggi’s disappearance.

The United States is seeking more information, a State Department said. “We are not in a position to confirm these reports, but we are following them closely,” the official said.

Khashoggi’s fiancee could not immediately be contacted but she said in a Tweet that there had been no official confirmation of the Turkish sources’ statements. “Jamal was not killed and I do not believe he was killed,” Hatice Cengiz posted.

Another Turkish security source told Reuters that a group of 15 Saudi nationals, including some officials, had arrived in Istanbul in two planes and entered the consulate on the same day Khashoggi was there, and later left the country.

The source said Turkish officials were trying to identify them. Turkey’s Anadolu news agency also reported that the group of Saudis were briefly at the consulate.

DEEPENING DIVISIONS

Khashoggi’s disappearance is likely to further deepen divisions between Turkey and Saudi Arabia. Relations were already strained after Turkey sent troops to the Gulf state of Qatar last year in a show of support after its Gulf neighbours, including Saudi Arabia, imposed an embargo on Doha.

Turkish President Tayyip Erdogan, whose AK Party is rooted in political Islam, also supported a government in Egypt led by the Muslim Brotherhood, which Saudi Arabia has designated a terrorist movement.

Saudi Arabia’s Crown Prince Mohammed bin Salman said this week that the kingdom would allow Turkey to search the consulate for Khashoggi. But he also criticized Turkey’s crackdown following a 2016 failed coup against Erdogan.

On Saturday, Yasin Aktay, Erdogan’s AK Party adviser and a friend of Khashoggi, told Qatari broadcaster Al Jazeera: “We demand a convincing clarification from Saudi Arabia, and what the crown prince offered is not convincing.”

He also said what happened to Khashoggi was a crime and those responsible for his disappearance must be tried, Al Jazeera said.

Khashoggi is a familiar face on political talk shows on Arab satellite television networks and used to advise Prince Turki al-Faisal, former Saudi intelligence chief and ambassador to the United States and Britain.

Over the past year, he has written columns for newspapers including the Washington Post criticising Saudi policies towards Qatar and Canada, the war in Yemen and a crackdown on dissent which has seen dozens of people detained.

“I have left my home, my family and my job, and I am raising my voice,” he wrote in September. “To do otherwise would betray those who languish in prison. I can speak when so many cannot.”

Two months later, writing about the detentions of scores of Saudi royals, senior officials and businessmen accused of corruption, he said Mohammed bin Salman dispensed “selective justice” and said there was “complete intolerance for even mild criticism” of the crown prince.

The Committee to Protect Journalists said it was alarmed by reports Khashoggi may have been killed inside the consulate.

“The Saudi authorities must immediately give a full and credible accounting of what happened to Khashoggi inside its diplomatic mission,” CPJ said in a statement. (Additional reporting by Sarah Dadouch, Tuvan Gumrukcu and Dominic Evans in Istanbul, Yara Bayoumy and Lesley Wroughton in Washington; Editing by Nick Tattersall)